Semiconductor device embedded with pressure sensor and manufacturing method thereof

ABSTRACT

The method for promoting the size reduction, the performance improvement and the reliability improvement of a semiconductor device embedded with pressure sensor is provided. In a semiconductor device embedded with pressure sensor, a part of an uppermost wiring is used as a lower electrode of a pressure detecting unit. A part of a silicon oxide film formed on the lower electrode is a cavity. On a tungsten silicide film formed on the silicon oxide film, a silicon nitride film is formed. The silicon nitride film has a function to fill a hole or holes and suppress immersion of moisture from outside to the semiconductor device embedded with pressure sensor. A laminated film of the silicon nitride film and the tungsten silicide film forms a diaphragm of the pressure sensor.

CROSS-REFERENCE RELATED APPLICATION

This application is a Continuation of nonprovisional U.S. applicationSer. No. 11/237,897 filed on Sep. 29, 2005. Priority is claimed based onU.S. application Ser. No. 11/237,897 filed on Sep. 29, 2005, whichclaims priority from Japanese Patent Applications 2004-289476 filed onOct. 1, 2004 and 2005-284013 filed on Sep. 29, 2005, the contents ofwhich are hereby incorporated by reference into this application.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a semiconductor device embedded withpressure sensor and a manufacturing method thereof. More particularly,the present invention relates to a technology effectively applied to thesize reduction of a semiconductor device embedded with pressure sensorand the performance enhancement thereof.

BACKGROUND OF THE INVENTION

Pressure sensors are sensors used in various fields. Of these, thedemands for a small-sized pressure sensor formed by using MEMS (MicroElectro Mechanical Systems) manufacturing technologies or semiconductormicrofabrication technologies have been increasing rapidly. For example,for industrial use, such sensors have been applied to pressure controland monitoring of various types of plant equipment. For consumer use,they have been used for gas meters, flowmeters, sphygmomanometers, andothers. For automobile, they have been used for engine or brake control,tire pressure monitoring, and others.

In view of means for detecting pressure, the small-sized pressuresensors can be classified into those of a piezoresistance type that usea piezoresistive element embedded in a diaphragm to detect a deflectionof the diaphragm caused by pressure, those of a capacitance type thatdetect a distance between two electrodes varying by pressure as a changein capacitance, those of a resonator type that detect a change inresonance frequency of a resonator caused by a change in pressure, andothers.

On the other hand, as pressure sensors directed to the purposes otherthan those of the small-sized pressure sensors mentioned above,pressure-sensitive sensors have also been increasingly developed. Such asensor is mounted on the head or leg portion of a pet robot, forexample, for use in detecting a contact with a human. The sensor issometimes used at the input unit of an input device for adjusting therotation speed of a motor or the sound volume of a speaker. Thepressure-sensitive sensor detects a pressure by means of apressure-sensitive conductive film, for example. The value of theresistance of the pressure-sensitive conductive film varying inaccordance with a deformation by pressure is detected.

Note that one example of the pressure-sensitive sensor using apressure-sensitive conductive film is disclosed in Japanese PatentLaid-Open Publication No. 9-17276 (Patent Document 1). Also, one exampleof the pressure-sensitive conductive film and the manufacturing methodthereof are disclosed in Japanese Patent Laid-Open Publication No.2000-299016 (Patent Document 2).

Particularly in a small-sized pressure sensor for automobiles, demandsfor size reduction, performance enhancement, and cost reduction aregenerally strong. Especially, the reduction in size and weight isparticularly important for a pressure detecting unit used in a tirepressure monitoring system (TPMS), due to its characteristics of beinginstalled in a tire for a long time. Also, since power is often fedthrough a button battery, low power consumption is also desired. In theinitial stage of the practical use of the sensors, a method in whichcomponents including a piezoresistive monolithic pressure sensor, asemiconductor device for signal processing, a wireless semiconductordevice, a button battery and others are mounted on a small-sized printedboard was used. However, due to problems such as high cost and largepower consumption leading to a short battery life, such a method has notyet been widespread.

For the achievement of size reduction, low power consumption and lowcost, it is effective to accomodate, in addition to the monolithicpressure sensor, peripheral semiconductor devices required forprocessing and transmitting a signal from the sensor in a singlepackage, and further, in a single chip. This has been actively studied.

The single-packaging has been achieved by mounting a piezoresistivepressure sensor or the like and a semiconductor device having a functionto amplify a signal from the sensor and other functions in a singlepackage by using a mounting technology. An example of suchsingle-packaging is disclosed in J. Dancaster et al., “TWO-CHIP PRESSURESENSOR AND SIGNAL CONDITIONING”, TRANSDUCERS '03 (The 12th InternationalConference on Solid State Sensors, Actuators and Microsystems, Boston,Jun. 9-12 2003) proceedings, pp. 1669-1702 (Non-patent Document 1).Since this single-packaging allows the pressure sensor and thesemiconductor device to be manufactured separately, each devicestructure and manufacturing process does not have to be changed, whichis advantageous. However, since the pressure sensor and a part of thesemiconductor devices are simply packaged as one, it is difficult toachieve the cost reduction. Although a piezoresistive pressure sensorfrom which a large output signal can be obtained is often used, such apiezoresistive pressure sensor requires large power consumption. In thenon-patent document 1, effects of low power consumption achieved throughthe contrivance on the circuitry are described. However, effects of lowpower consumption achieved by the single-packaging itself is consideredto be small.

On the other hand, the single-chip has been achieved by a manufacturingmethod in which two substrates are bonded together. A recent example ofsuch a method is described in detail in Abhijeet V. Chavan et al., “AMonolithic Fully-Integrated Vacuum-sealed CMOS Pressure SENSOR”, IEEETRANSACTIONS ON ELECTRON DEVICES, VOL. 49, NO. 1, JANUARY 2002, pp.164-169 (Non-patent Document 2). In this method, a substrate on which atleast a part of a pressure sensor is formed and a substrate on which asemiconductor device or the like is formed are bonded together by meansof anodic bonding or the like to form one substrate. Another exemplarymethod is a manufacturing method in which, after a semiconductor deviceis formed on the perimeter of a semiconductor chip, the rear surface atthe center portion of the chip is processed into a thin film by theetching using potassium hydroxide to form a diaphragm, and a glasssubstrate is laminated on the rear surface side to form a vacuum cavityportion. In either case, for saving the manufacturing effort andreducing the cost, a method of bonding during a substrate stage beforedicing is generally taken. Thereafter, by dicing the bonded substrates,a pressure sensor and a semiconductor device are embedded in one chip.What is used in the Non-patent Document 2 is a capacitive pressuresensor. Since the single-chip made by this method can shorten the wiringlength between the pressure sensor and the detecting circuit, acapacitive sensor required to detect a minute change in capacitance canbe applied. However, similar to the above-described single-packaging,the single-chip made by this method has a limitation on the costreduction.

A method having a higher possibility for suppressing manufacturing costand achieving further size reduction and low power consumption than thatof the above-described single-packaging or single-chip made by bondingsubstrates is a method of forming both of a pressure sensor and asemiconductor device together on a semiconductor substrate, with acontrivance on device structure and manufacturing process. Depending onthe combination of the type of the pressure sensor and the semiconductordevice for realizing a single-chip, some contrivance will be requiredfor the device structure and the manufacturing process. Methods offorming a capacitive pressure sensor while manufacturing a semiconductordevice are disclosed in U.S. Pat. No. 6,472,243 (Patent Document 3),Klaus Kasten et al., “CMOS-compatible capacitive high temperaturepressure sensors”, Sensors and Actuators 85 (2000), pp. 147-152(Non-patent Document 3), and Klaus Kasten et al., “High temperaturepressure sensor with monolithically integrated CMOS readout circuitbased on SIMOX technology”, The 11th International Conference onSolid-State Sensors and Actuators (Munich, Germany, Jun. 10-14, 2001)proceedings, pp. 510-513 (Non-patent Document 4). With thesemanufacturing methods, some products in which CMOS (Complementary MetalOxide Semiconductors) including analog/digital combined circuits such asa temperature sensor for temperature compensation, an analog-digitalconverter circuit, a logic circuit, a clock and a power supply controlcircuit are combined in addition to the pressure sensor in one chip havealready been in practical use. In some cases, non-volatile memory suchas EEPROM (Electrically Erasable and Programmable Read Only Memory) forstoring calibration data or the like may be also embedded.

In the conventional technologies described in Patent Document 3 and U.S.Pat. No. 5,596,219 (Patent Document 4), Non-patent Document 3 and 4, andT. Bever et al., “Solutions for The Pressure Monitoring Systems”, 7thInternational Conference on Advanced Microsystems for AutomotiveApplications 2003 (Berlin, Germany, May 22-23, 2003) proceedings, pp.261-269 (Non-patent Document 5), a polycrystalline silicon layer is usedas a diaphragm serving as an upper electrode of a capacitor forobtaining a capacitance in accordance with the pressure. As a lowerelectrode, another polycrystalline silicon layer different from adiaphragm formed on a diffusion layer in the substrate or a field oxidefilm is used.

The reason why the conventional technologies select the above structureis to form a capacitor having a shape close to that of a parallel platecapacitor. To ensure durability of the diaphragm and approximate acapacitor with its capacitance varying linearly with respect topressure, a parallel plate capacitor is considered to be mostadvantageous.

In general, in the course of manufacturing a semiconductor device, thetopography gets less planar. In some cases, a planarization process maybe inserted to achieve more planar topography. However, in a generalmethod of manufacturing a semiconductor device particularly with itscritical dimension larger than 0.5 μm, even if local nonplanartopography are mitigated, nonplanar topography in a large area such asthat required by a capacitor are not resolved. That is, it is extremelydifficult to form a parallel plate capacitor on an upper portion where asemiconductor element such as a transistor has been once formed. When apressure sensor is embedded together with the semiconductor deviceproduced by such a manufacturing method, there is no other way but tosecure a flat area on the diffusion layer or the field oxide film andthen form a capacitor for detecting pressure thereon.

One reason for using a polycrystalline silicon layer as the electrodematerial is that the electrode can be formed simultaneously during theprocess of forming a polycrystalline silicon layer serving as a gateelectrode or a resistive layer of a transistor. Also, since it isresistant to hydrofluoric acid, polycrystalline silicon can be used as amask when a silicon oxide layer between electrodes of the capacitor isetched, thereby advantageously making it easy to form the capacitor.Furthermore, since polycrystalline silicon has been studied for a longtime as a material for movable parts of MEMS, which film to be used forforming an excellent diaphragm has been greatly elucidated. Also at thispoint, polycrystalline silicon can be considered as an easy-to-usematerial.

SUMMARY OF THE INVENTION

The capacitive pressure sensor of the semiconductor device embedded withpressure sensor disclosed in Patent Document 3 and Non-patent Documents3 to 5 is more suitable for being embedded onto the same substrate asthat of the semiconductor device when compared with sensors of apiezoresistance type or an oscillator type. Even so, there are manymanufacturing limitations. The largest problem is that the reduction ofa chip area of the semiconductor device embedded with pressure sensor isdifficult.

In the semiconductor device embedded with pressure sensor disclosed inPatent Document 3 and Non-patent Documents 3 to 5, because of theabove-described structure, the sensor area and the semiconductor devicearea are completely separated on the substrate. Therefore, the chip areaamounts to a total of the semiconductor device area and the capacitorarea. Moreover, as described in Non-patent Documents 2 to 5, in order toperform highly accurate measurement with a capacitive pressure sensor,in addition to a capacitor for measurement, a reference capacitorserving as a reference of pressure and having the same structure isrequired. Although microfabrication of a semiconductor device can reducethe area occupied by the semiconductor device, the capacitance of thesecapacitors has to be large to some extent for highly accurate detectionof pressure. Thus, the reduction in capacitor area has a limitation. Asthe semiconductor device is more microfabricated, the ratio of the areaoccupied by the capacitors in the chip increases. The existence of thecapacitor area becomes a large restriction on reduction in chip area,thereby inhibiting the cost reduction of the semiconductor deviceembedded with pressure sensor.

Other than the above-described chip-area problem, the conventionaltechnologies have manufacturing limitations. In general, apolycrystalline silicon film formed by low pressure chemical vapordeposition (CVD) has an internal stress. A large internal stress maycause the characteristic of the diaphragm to be varied with time or maycause the life of the diagraph to be reduced. To get around theseproblems, the internal stress has to be reduced by, for example,inserting a heat treatment after film formation.

One method of releasing the stress of a polycrystalline silicon film isdescribed in detail in Patent Document 3. What is most concerned in thisconventional technology is an influence of the heat treatment forreleasing the stress of the diaphragm formed of polycrystalline siliconto be exerted on the transistor characteristic of the semiconductordevice. Since the heat treatment for releasing the stress is performedat high temperatures, there is a problem that the transistorcharacteristic is deteriorated if this heat treatment process isinserted after the transistor is formed. The method of manufacturing asemiconductor device embedded with pressure sensor disclosed in PatentDocument 3 shows a solution of the problem. By performing the activationanneal of the source and drain of the transistor and the anneal forreleasing the stress of the diaphragm simultaneously, an excessive heattreatment on the transistor can be avoided, thereby preventing thedeterioration in transistor performance.

However, as the semiconductor device is microfabricated more, control ofthe impurity distribution in the transistor is enhanced and thetemperature at a heat treatment for activating impurities is reduced. InPatent Document 3, it is preferable that heat treatment temperature is900 to 1100° C. and a heat treatment time is 20 to 40 seconds. However,a transistor resistant to such a severe heat treatment may be atransistor of a generation with a gate length of at least 1.3 μm orlonger. That is, it is obvious that, with the manufacturing methoddisclosed in Patent Document 1, the influence on the characteristic ofthe microfabricated transistor cannot be suppressed. In general, alongwith the development of the microfabrication, the performance ofsemiconductor device is enhanced and the cost thereof is decreased. Theimpossibility of the embedding with the microfabricated semiconductordevice greatly inhibits the performance enhancement and cost reductionof the semiconductor device embedded with pressure sensor.

In particular, in the semiconductor device embedded with pressure sensorfor use in a tire pressure monitoring system, the embedding of awireless circuit for transmitting and receiving a signal to and fromoutside of the tire is also required. To drive a wireless circuit withlow power, it can be thought that a somewhat high performance CMOStransistor is required and a transistor with at least a gate lengthequal to or shorter than 0.8 μm is required. Thus, in the aboveconventional technologies, even a wireless circuit cannot be embedded onone chip, and therefore, there is no other choice but to make anotherchip manufactured separately from the chip of the semiconductor deviceembedded with pressure sensor. This another chip can be mounted in thesame single package as that of the semiconductor device embedded withpressure sensor. However, as described above, effects of performanceincrease and cost reduction are small.

On the other hand, with some contrivance on the method and conditions offorming a polycrystalline silicon film, attempts have also been made toreduce the internal stress of the film even without performing a heattreatment at high temperatures after film formation. Furthermore, otherattempts have also been made to apply a silicon germanium film with lowstress to the structure of MEMS. When these films are used, arestriction occurs that a process at temperatures higher than those atthe time of film formation cannot be applied after film formation.Moreover, even a process at temperatures lower than those at the time offilm formation may have an influence on the internal stress of thediaphragm film. Therefore, optimization of the manufacturing method inconsideration of all processes after diaphragm film formation isrequired. Since the semiconductor device embedded with sensor cannot bemade by a manufacturing method common to other semiconductor devices,cost reduction of the semiconductor device embedded with sensor isinhibited.

Another problem of the conventional technologies is complexity inpackaging. In the above-described conventional technologies, since alower layer on the semiconductor substrate is used as a diaphragm of apressure sensor, an opening is required to be formed thereon on thesidewall of the opening, an interlayer insulating film or the like ofthe semiconductor device is exposed. To ensure reliability of thesemiconductor device even without a passivation film at the portion ofthe through hole, special packaging technology that allows the exposedpart to be protected from moisture, mobile ion, and the like isrequired, which leads to an increase in packaging cost. When used in atire pressure monitoring system, since resistance to a severeenvironment in the tire is required, the packaging problem becomes moreserious.

As described above, a first problem of the conventional technologies isthat there is a limitation on reduction of the chip area of thesemiconductor device embedded with pressure sensor. A second problemthereof is that the embedding of a pressure sensor poses a limitation onthe method of manufacturing a semiconductor device and a restriction onthe embeddable semiconductor devices. A third problem is that theembedding of a pressure sensor makes the packaging complicated.

An object of the present invention is to provide a technology capable ofreducing the size of a semiconductor device embedded with pressuresensor.

Another object of the present invention is to provide a technologycapable of achieving the greater functionality of a semiconductor deviceembedded with pressure sensor.

Still another object of the present invention is to provide a technologycapable of achieving the higher reliability of a semiconductor deviceembedded with pressure sensor.

The above and other objects and novel characteristics of the presentinvention will be apparent from the description of this specificationand the accompanying drawings.

The typical ones of the inventions disclosed in this application will bebriefly described as follows.

A method of manufacturing a semiconductor device embedded with pressuresensor according to the present invention is characterized in that, byapplying a planarization process of an insulating film by the CMP to asemiconductor device manufacturing process, a pressure detecting unitcan be formed on an upper layer of the semiconductor device, and theupper two conductive layers are used for the pressure detecting unit.

That is, after an insulating film on a high-performance analog/digitalcombined circuit and/or a non-volatile memory circuit formed of MOStransistors formed on a semiconductor substrate is planarized by thechemical-mechanical polishing, a pressure detecting unit included in apressure sensor on the above-mentioned circuit is formed. By doing so, asemiconductor device embedded with pressure sensor with low powerconsumption and a small chip area can be realized.

There are two types of the structure of the pressure detecting unit.First is that upper two conductive layers are used as capacitorelectrodes and second is that the two layers of a pressure-sensitiveconductive film and an electrode lower than that film are used ascapacitor electrodes. It is also possible to form at least a part of thesemiconductor device on a lower layer of the pressure detecting unit.

The effect obtained by the representative one of the inventionsdisclosed in this application will be briefly described as follows.

Since a semiconductor device can be formed on a layer located lower thana pressure detecting unit, the chip area of the semiconductor deviceembedded with pressure sensor can be reduced. In particular, when apressure detecting unit using a pressure-sensitive conductive film isapplied, unlike a capacitance type, it is enough to connect two or moreelectrodes from only the lower layers of the pressure detecting unit tothe pressure-sensitive conductive film. This is advantageous in that asemiconductor device embedded with pressure sensor can be manufacturedsignificantly easily. Also, other than the application and change of aplanarization process to be performed according to need, no influence isexerted on semiconductor devices located lower than the pressuredetecting unit. Therefore, no limitation occurs on the semiconductordevice manufacturing method. Consequently, it is possible to embed ahighly-microfabricated high-performance semiconductor device and apressure sensor, and as a result, the low power consumption can beachieved. Furthermore, since the pressure detecting unit is formed on anupper layer of a semiconductor device and the semiconductor device isprotected by a nitride film or a polyimide film, it becomes possible tosimplify the packaging more than that in the conventional technologies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view of main components including a pressuredetecting unit of a semiconductor device embedded with pressure sensoraccording to an embodiment of the present invention;

FIG. 2 is a section view of main comments including a referencecapacitor unit of the semiconductor device embedded with pressure sensoraccording to an embodiment of the present invention;

FIG. 3 is a section view of main components including an analog circuitunit of the semiconductor device embedded with pressure sensor accordingto an embodiment of the present invention;

FIG. 4 is a section view of main components including a flash memorycircuit unit of the semiconductor device embedded with pressure sensoraccording to an embodiment of the present invention;

FIG. 5 is a section view of main components including a pad portion ofthe semiconductor device embedded with pressure sensor according to anembodiment of the present invention;

FIG. 6 is a plan view of the semiconductor device embedded with pressuresensor after wire bonding;

FIG. 7 is a section view of the semiconductor device embedded withpressure sensor taken along the line A-A of FIG. 6;

FIG. 8 is a section view of the semiconductor device embedded withpressure sensor taken along the line B-B of FIG. 6;

FIG. 9 is a section view of a package in which the semiconductor deviceembedded with pressure sensor according to an embodiment of the presentinvention is packaged;

FIG. 10 is a plan view of a printed circuit board for a tire pressuremonitoring system in which the semiconductor device embedded withpressure sensor according to an embodiment of the present invention ispackaged;

FIG. 11 is a plan view of a printed circuit board for a tire pressuremonitoring system including a package in which a conventionalsemiconductor device embedded with pressure sensor is packaged;

FIG. 12 is a section view of a pressure detecting unit of a conventionalsemiconductor device embedded with pressure sensor;

FIG. 13 is a section view showing a method of manufacturing asemiconductor device embedded with pressure sensor according to anembodiment of the present invention;

FIG. 14 is a section view showing the method of manufacturing asemiconductor device embedded with pressure sensor subsequent to FIG.13;

FIG. 15 is a section view showing the method of manufacturing asemiconductor device embedded with pressure sensor subsequent to FIG.14;

FIG. 16 is a section view showing the method of manufacturing asemiconductor device embedded with pressure sensor subsequent to FIG.15;

FIG. 17 is a section view showing the method of manufacturing asemiconductor device embedded with pressure sensor subsequent to FIG.16;

FIG. 18 is a section view showing the method of manufacturing asemiconductor device embedded with pressure sensor subsequent to FIG.17;

FIG. 19 is a section view showing the method of manufacturing asemiconductor device embedded with pressure sensor subsequent to FIG.18;

FIG. 20 is a section view showing the method of manufacturing asemiconductor device embedded with pressure sensor subsequent to FIG.19;

FIG. 21 is a section view showing the method of manufacturing asemiconductor device embedded with pressure sensor subsequent to FIG.20;

FIG. 22 is a section view showing the method of manufacturing asemiconductor device embedded with pressure sensor subsequent to FIG.21;

FIG. 23 is a section view showing the method of manufacturing asemiconductor device embedded with pressure sensor subsequent to FIG.22;

FIG. 24 is a graph showing a pressure-capacitance characteristic of thesemiconductor device embedded with pressure sensor according to anembodiment of the present invention;

FIG. 25 is a graph showing the characteristic between the number oftimes of pressuring and capacitance change of the semiconductor deviceembedded with pressure sensor according to an embodiment of the presentinvention;

FIG. 26 is a plan view showing a layout of an uppermost layer wiring ofthe semiconductor device embedded with pressure sensor according to anembodiment of the present invention;

FIG. 27 is another plan view showing the layout of the uppermost layerwiring of the semiconductor device embedded with pressure sensoraccording to an embodiment of the present invention;

FIG. 28 is still another plan view showing the layout of the uppermostlayer wiring of the semiconductor device embedded with pressure sensoraccording to an embodiment of the present invention;

FIG. 29 is a section view of main components including a pressuredetecting unit of a semiconductor device embedded with pressure sensoraccording to another embodiment of the present invention;

FIG. 30 is a section view showing a method of manufacturing asemiconductor device embedded with pressure sensor according to stillanother embodiment of the present invention;

FIG. 31 is a section view showing the method of manufacturing asemiconductor device embedded with pressure sensor subsequent to FIG.30;

FIG. 32 is a section view showing the method of manufacturing asemiconductor device embedded with pressure sensor subsequent to FIG.31;

FIG. 33 is a section view showing a method of manufacturing asemiconductor device embedded with pressure sensor according to stillanother embodiment of the present invention;

FIG. 34 is a section view showing the method of manufacturing asemiconductor device embedded with pressure sensor subsequent to FIG.33;

FIG. 35 is a section view showing the method of manufacturing asemiconductor device embedded with pressure sensor subsequent to FIG.34;

FIG. 36 is a section view showing the method of manufacturing asemiconductor device embedded with pressure sensor subsequent to FIG.35;

FIG. 37 is a section view showing the method of manufacturing asemiconductor device embedded with pressure sensor subsequent to FIG.36;

FIG. 38 is a section view of main components including a pressuredetecting unit of a semiconductor device embedded with pressure sensoraccording to still another embodiment of the present invention;

FIG. 39 is a section view of main components including a pressuredetecting unit of a semiconductor device embedded with pressure sensoraccording to still another embodiment of the present invention; and

FIG. 40 is a plan view of an electrode layout of the semiconductordevice embedded with pressure sensor shown in FIG. 39.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. Note that componentshaving the same function are denoted by the same reference symbolsthroughout the drawings for describing the embodiment, and therepetitive description thereof will be omitted.

First Embodiment

In the first embodiment, the present invention is applied to asemiconductor device embedded with pressure sensor in which a digitalcircuit, an analog circuit such as an amplifier for amplifying a sensorsignal and a wireless transceiver circuit, a flash memory circuit of aMONOS (Metal Oxide Nitride Oxide) type, a capacitive pressure sensor andthe like are embedded together on one chip.

FIG. 1 is a section view of main components including a pressuredetecting unit of a semiconductor device embedded with pressure sensoraccording to the first embodiment. On the surface of a silicon substrate1, a trench isolation 2 is formed, and MOS (Metal Oxide semiconductor)transistors (Qn, Qp) having a gate oxide film 3, a gate electrode 4formed of a polycide film, a cap insulating film 5, a side wall 6, andothers are formed. The n channel type MOS transistor (Qn) is formed on ap type well 7, and the p channel type MOS transistor (Qp) is formed onan n type well 8. The minimum gate length of the MOS transistors (Qn,Qp) is 0.35 μm.

On the upper portion of the MOS transistors (Qn, Qp), a silicon oxidefilm 11 is formed. On each of the upper portion of a diffusion layer(source, drain) 9 of the MOS transistor (Qn) and the upper portion of adiffusion layer (source, drain) 10 of the MOS transistor (Qp), a contacthole 12 is formed. Inside the contact hole 12, a plug 13 formed of atitanium nitride film and a tungsten film is formed.

On the upper portion of the silicon oxide film 11, a first layer wiring14 connected to the plug 13 is formed. The first layer wiring 14 isformed of a titanium nitride film, an aluminum alloy film, a titaniumnitride film, and a titanium film in this order from above. On the upperportion of the first layer wiring 14, a second layer wiring 16 connectedto the first layer wiring 14 via a via hole 15, a third layer wiring 18connected to the second layer wiring 16 via a via hole 17, a fourthlayer wiring 20 connected to the third layer wiring 18 via a via hole19, and a fifth layer wiring 22 connected to the fourth layer wiring 20via a via hole 21 are formed. Similar to the first layer wiring 14, eachof the second layer wiring 16 to the fifth layer wiring 22 is formed ofa titanium nitride film, an aluminum alloy film, a titanium nitridefilm, and a titanium film.

The first layer wiring 14 to the fifth layer wiring 22 are insulatedfrom each other by interlayer insulating films 23 made of silicon oxide.In the manufacture of a semiconductor device according to thisembodiment, the CMP is used at the key steps. Therefore, each of thefirst layer wiring 14 to the fifth layer wiring 22 is formed to beapproximately flat, and also the surface of the fifth layer wiring 22 isapproximately flat.

In the semiconductor device embedded with pressure sensor according tothis embodiment, a part of the fifth layer wiring 22 is used as a lowerelectrode 22 a of a pressure detecting unit. A part of silicon oxidefilm 24 formed on the lower electrode 22 a is a cavity 25, and thecavity 25 is filled with gas at approximately 1 atmospheric pressurecontaining nitrogen as the main component. A part of a tungsten silicidefilm 26 formed on the silicon oxide film 24 has holes 27, through whichhydrofluoric acid is introduced to form the cavity 25 in the siliconoxide film 24.

On the tungsten silicide film 26, a silicon nitride film 28 formed byplasma CVD (Chemical Vapor Deposition) is formed. The silicon nitridefilm 28 has a function to fill the holes 27 and suppress the immersionof moisture from outside into the semiconductor device embedded withpressure sensor. In this embodiment, the laminated layer of the siliconnitride film 28 and the tungsten silicide film 26 serves as a diaphragm.The tungsten silicide film 26 which forms a part of the diaphragm isconnected to the fifth layer wiring 22 via a via hole 45. On the upperlayer of a part of the silicon nitride film 28, a silicon oxide film 29,a silicon nitride film 30, and a photosensitive polyimide film 31 areformed.

Each of the part of the MOS transistors (Qn, Qp) and the first layerwiring 14 to the fifth layer wiring 22 form a digital circuit. Since apart of the fifth layer wiring 22 is connected to the diaphragm of thepressure detecting unit and the lower electrode 22 a, it forms a part ofan analog circuit. However, except for a wiring that connects betweenelectrodes, the pressure detecting unit is not located on the analogcircuit, but is formed on the digital circuit. This is in order toprevent the electrical charge stored in a capacitor of the pressuredetecting unit from causing the noise on the analog circuit so as toachieve the pressure detection with high accuracy.

FIG. 2 is another section view, different from FIG. 1, of thesemiconductor device embedded with pressure sensor according to thisembodiment. This section includes a reference capacitor unit. Thesilicon substrate 1 to the fifth layer wiring 22 and further to thediaphragm formed of the silicon nitride film 28 and the tungstensilicide film 26 are similar to those of the pressure detecting unitshown in FIG. 1. A major difference from the pressure detecting unitshown in FIG. 1 is that the photosensitive polyimide film 31, thesilicon nitride film 30, and the silicon oxide film 29 on the diaphragmare not removed. Therefore, the reference capacitor unit does notdirectly suffer from variations by outer pressure. Each part of the MOStransistors (Qn, Qp) and the first layer wiring 14 to the fifth layerwiring 22 on this section form a digital circuit.

Since a part of the fifth layer wiring 22 is connected to the lowerelectrode 22 a of the reference capacitor, it forms a part of an analogcircuit. However, except for a wiring that connects between electrodes,the pressure detecting unit is not located on the digital circuit, andthe reference capacitor unit is not located on the digital circuit. Thisis in order to prevent the electrical charge stored in a capacitor ofthe reference capacitor unit from causing the noise on the analogcircuit so as to achieve the pressure detection with high accuracy.

FIG. 3 is still another section view, different from FIG. 1 and FIG. 2,of the semiconductor device embedded with pressure sensor according tothis embodiment. This section is a section of the analog circuit unit,and each of the MOS transistors (Qn, Qp) and the first layer wiring 14to the fifth layer wiring 22 form the analog circuit. The top of thefifth layer wiring is covered with the silicon nitride film 30 and thephotosensitive polyimide film 31.

FIG. 4 is still another section view, different from FIG. 1 to FIG. 3,of the semiconductor device embedded with pressure sensor according tothis embodiment. This section is a section of a flash memory circuitunit, and the first layer wiring 14, the second layer wiring 16 and thethird layer wiring 18 are formed on a MONOS-type flash memory transistor(Qf) having a memory gate 40 and a control gate 41. Since the controlgate 41 is formed at the same time when the gate electrode 4 composed ofa polycide film is formed, it has the same film thickness as that of thegate electrode 4 in practice.

In the flash memory circuit unit, only the above-mentioned three of fivelayer wirings (first layer wiring 14 to fifth layer wiring 22) are used.Therefore, although the upper wiring layers can be used as a pressuredetecting unit and/or a reference capacitor unit, no pressure detectingunit or reference capacitor is disposed on the flash memory circuit inthis embodiment because memory capacity to be mounted is small. Apressure detecting unit and/or a reference capacitor may be formed onthe flash memory circuit.

FIG. 5 is still another section view, different from FIG. 1 to FIG. 4,of the semiconductor device embedded with pressure sensor according tothis embodiment. This section is a section including a pad portion.Since the CMP is used at the key steps in the course of themanufacturing process of the semiconductor device in this embodiment,the wiring layers are approximately planarized. However, even in manyother semiconductor devices manufactured without using the CMP, the padportion is often flat. In this embodiment, no pressure detecting unit orreference capacitor is disposed on a pad 50, but a pressure detectingunit and/or reference capacitor may be formed on the pad 50.

On the upper portion of the polycide film 4 a, the pad 50 is formed of astack of the first layer wiring 14 to the fifth layer wiring 22 andthese wiring layers are connected to each other via many via holes andthe like in many cases. Since FIG. 5 shows a section not including viaholes, these via holes are not shown. On the surface of the pad 50, ofthe materials forming the fifth layer wiring 22, the titanium nitridefilm of the uppermost layer is removed by the etching, and the aluminumalloy layer is exposed. The periphery of the pad 50 is covered with thesilicon nitride film 30 and the photosensitive polyimide film 31.

FIG. 6 is a view of the semiconductor device embedded with pressuresensor according to this embodiment viewed from the top after wirebonging. Openings 32 are formed in a part of the photosensitivepolyimide film 31 on the surface of the semiconductor device, and thediaphragms of the pressure detecting units are exposed on the bottomportion of the openings 32. Also, on the other area of thephotosensitive polyimide film 31, pads 50 for bonding are exposed, andgold wires 33 are connected to the surface of the pads 50.

FIG. 7 is a section view of the semiconductor device embedded withpressure sensor taken along the line A-A of FIG. 6. An area at the leftend represents the analog circuit unit, two areas at the centerrepresent the pressure detecting unit, and an area at the right endrepresents the pad portion. Except the pressure detecting unit and thepad portion, the areas are covered with the silicon nitride film 30 andthe photosensitive polyimide film 31. The top of the diaphragm of thepressure detecting unit is covered with the silicon nitride film 28.

FIG. 8 is a section view of the semiconductor device embedded withpressure sensor taken along the line B-B of FIG. 6. An area at the leftend represents the flash memory circuit unit, two areas at the centerrepresent the reference capacitor unit, and an area at the right endrepresents the pad portion. Except the pad portion connected with thegold wire 33, the areas including the top of the diaphragm of thereference capacitor unit are covered with the silicon nitride film 30and the photosensitive polyimide film 31.

FIG. 9 is a section view of a package having the semiconductor deviceembedded with pressure sensor implemented thereon according to thisembodiment. A semiconductor device embedded with pressure sensor 60 isfixed onto a die pad portion 61 and is electrically connected to a lead62 by the gold wire 33. This package 67 is a plastic-mold-type packageusing a cylinder 63, and the semiconductor device embedded with pressuresensor 60 and the gold wire 33 are sealed by mold resin 64. The insideof the cylinder 63 is filled with silicone gel 65, and its surface isfilled by a resin film 66. This resin film 66 is deformed by pressureapplied from outside to add pressure on the silicone gel 65. Then, thepressure transmitted via the silicone gel 65 is detected by the pressuredetecting unit of the semiconductor device embedded with pressure sensor60.

FIG. 10 is a plan view of a printed circuit board for a tire pressuremonitoring system having the semiconductor device embedded with pressuresensor implemented thereon according to this embodiment. On a printedcircuit board 70, a button battery 71 is fixed. The button battery 71 iselectrically connected to the printed circuit board 70 via a terminal72. Also, on the printed circuit board 70, the package 67 shown in FIG.9, a crystal resonator 73, a passive elements 74 for an RF circuit, andthe like are implemented. On an opposite surface of the printed circuitboard 70, an antenna (not shown) is provided.

On the other hand, FIG. 11 is a plan view of a printed circuit board fora tire pressure monitoring system including a package having aconventional semiconductor device embedded with pressure sensorimplemented thereon. On a printed circuit board 76, a button battery 77is fixed. The button battery 77 is electrically connected to the printedcircuit board 76 via a terminal 78. Also, on the printed circuit board76, a package 79 in which a conventional semiconductor device embeddedwith pressure sensor having an opening for detecting pressure whosesurface is sealed by a film 75, a package 80 accommodating asemiconductor device provided with a wireless circuit unit and asemiconductor device provided with a digital circuit unit or the like,the crystal resonator 73, passive elements 74 for an RF circuit, and thelike are implemented. On an opposite surface of the printed circuitboard 76, an antenna (not shown) is provided.

When comparing the sizes of the printed circuit board 70 of FIG. 10 onwhich the semiconductor device embedded with pressure sensor 60according to this embodiment is implemented and the printed circuitboard 76 of FIG. 11 on which the conventional semiconductor deviceembedded with pressure sensor is implemented, the printed circuit board70 is approximately one-third smaller then the printed circuit board 76.This is because, since the integration degree of the semiconductordevice embedded with pressure sensor 60 according to this embodiment ishigher, components corresponding to the package 80 of FIG. 11 are notnecessary, and since the semiconductor device embedded with pressuresensor 60 according to this embodiment requires lower power consumption,the capacity of the button battery 71 required for obtaining the samelife can be small. The button battery 77 has a capacity of anapproximately half of that of the button battery 71, and therefore, itssize and thickness are smaller accordingly. As described above,according to this embodiment, the small-sized printed circuit board 70for a tire pressure monitoring system with low power consumption can beachieved.

FIG. 12 is a section view of a pressure detecting unit of theconventional semiconductor device embedded with pressure sensor. On thesurface of a silicon substrate 81, a silicon oxide film 82 is formed,and a silicon nitride film 83 is formed thereon. A lower electrode 84fixed onto the silicon nitride film 83 and a diaphragm 85 are bothformed of polycrystalline silicon films doped with impurities. A spacebetween the lower electrode 84 and the diaphragm 85 is vacuum. A hole 86once opened in a part of the diaphragm 85 in the course of themanufacturing process is filled with a silicon nitride film 87 and asilicon oxide film 88 formed on the diaphragm 85.

On the silicon oxide film 88, an interlayer insulating film 89 made of asilicon oxide based material is formed. However, this interlayerinsulating film 89 is removed only on the upper portion of the diaphragm85 and an opening portion 90 is formed. Since the interlayer insulatingfilm 89 is exposed on the sidewall of the opening portion 90, there is apossibility that moisture comes into the diaphragm 85. For itsprevention, special contrivance is required for the packaging of thesemiconductor device embedded with pressure sensor. Therefore, themanufacturing cost is increased.

The printed circuit board 70 shown in FIG. 10 and the printed circuitboard 76 shown in FIG. 11 are installed in an environment simulating theinside of a tire by the same packaging technology to evaluate life andstability. As a result, the printed circuit board 70 using thesemiconductor device embedded with pressure sensor 60 according to thisembodiment has a longer life and better stability. The life is evaluatedwith acceleration in an environment at high temperature and humidity.When the printed circuit board 76 having the semiconductor deviceembedded with pressure sensor implemented thereon of the conventionaltechnology is used, the life is as short as less than ten years inactual use conditions. On the other hand, in the case of the printedcircuit board 70 having the semiconductor device embedded with pressuresensor 60 according to this embodiment implemented thereon, the lifelonger than ten years is obtained.

Also, in the printed circuit board 76 provided with the conventionalsemiconductor device embedded with pressure sensor, change with time isobserved in the pressure detection. On the other hand, in the printedcircuit board 70 provided with the semiconductor device embedded withpressure sensor 60 according to the present invention, no change withtime is observed. This difference therebetween is thought to occur dueto the following reason. The semiconductor device embedded with pressuresensor 60 according to this embodiment has its surface protected by thesilicon nitride film 30 and the photosensitive polyimide film 31. On theother hand, in the conventional semiconductor device embedded withpressure sensor shown in FIG. 12, the diaphragm 85 for detectingpressure is near the silicon substrate 81, and the opening portion 90from the surface of the semiconductor device to the diaphragm 85 isformed. Since the sidewall of the opening portion 90 is not protected bya silicon nitride film or a photosensitive polyimide film, moisture inthe tire might permeate the semiconductor device to shorten the life ofthe semiconductor device and reduce the stability. As described above,according to this embodiment, the semiconductor device embedded withpressure sensor 60 with long life, high accuracy and stability, theprinted circuit board 70 for a tire pressure monitoring system andfurther a tire pressure monitoring system can be achieved.

Next, a method of manufacturing a semiconductor device embedded withpressure sensor according to this embodiment will be described withreference to FIG. 13 to FIG. 23. A critical dimension of thesemiconductor device embedded with pressure sensor is 0.35 μm.

First, a trench isolation 2 is formed on a main surface of a siliconsubstrate 1 shown in FIG. 13 by using the STI (Shallow Trench Isolation)technology, and then, photolithography technology and ion implantationtechnology are used to implant phosphorus ions in an n type well formingarea and implant boron ions in a p type well forming area. Subsequently,with a heat treatment at 1050° C. for 60 minutes, impurities implantedin the silicon substrate 1 are diffused and activated to form a p typewell 7 and an n type well 8. Note that an area at the left end in FIG.13 represents the flash memory circuit unit, two areas at the centerrepresent the pressure detecting unit, and an area at the right endrepresents the pad portion. Also, the isolation method is not limited toa method using the trench isolation 2, but may be a method using a fieldinsulating film formed by a LOCOS (Local oxidation of silicon) method.

Next, a silicon oxide film, a silicon nitride film, and a silicon oxidefilm are laminated on the silicon substrate 1 to form an ONO film 42.The silicon oxide film of the lower layer is formed by thermal oxidationof the surface of the silicon substrate 1, and the silicon nitride filmis formed by the low pressure CVD, and the silicon oxide film of theupper layer is formed by thermal oxidation of the surface of the siliconnitride film. The silicon oxide film of the lower layer has a thicknessof 1.5 nm.

Next, a polycrystalline silicon film having a thickness of 200 nm and acap insulating film 44 are deposited on the ONO film 42. Thepolycrystalline silicon film is formed by the low pressure CVD withusing monosilane as a source material. The substrate temperature is setat 650° C. After the ion implantation of phosphorus into thepolycrystalline silicon film, a heat treatment for activating thepolycrystalline silicon film is performed in nitrogen atmosphere. Theheat treatment temperature is 900° C., and the heat treatment time is 30minutes. At this time, crystal grains in the polycrystalline siliconfilm grow to become large. The cap insulating film 44 is formed of alaminated film of a silicon oxide film and a silicon nitride filmdeposited by the low pressure CVD. The substrate temperature at the timeof forming the cap insulating film 44 is 800° C. at maxinum.

Next, after the dry etching of the cap insulating film 44 with using aphotoresist film as a mask, the polycrystalline silicon film isdry-etched with using the cap insulating film 44 as a mask. By doing so,the memory gate 40 of the MONOS-type flash memory is formed on the ONOfilm 42 of the flash memory circuit unit. At this time, in the areaother than the lower portion of the memory gate 40, the silicon nitridefilm which is a part of the ONO film 42 is exposed. Therefore, the lightoxidization is performed in oxygen atmosphere at 800° C. to oxidize theedge of the memory gate 40, and then, this silicon nitride film isremoved with using hot phosphoric acid.

Next, as shown in FIG. 14, the control gate 41 is formed on the flashmemory circuit unit, and the gate electrode 4 is formed on the digitalcircuit unit and the analog circuit unit.

The control gate 41 and the gate electrode 4 are formed in the manner asfollows. That is, the surface of the silicon substrate 1 is thermallyoxidized to form the gate oxide film 3, and then, a silicon oxide filmis formed by the low pressure CVD. Thereafter, by the anisotropicetching of this silicon oxide film, a sidewall 43 is formed on thesidewall of the memory gate 40.

Next, a polycide film 4 a formed of a polycrystalline silicon film dopedwith phosphorus and a tungsten silicide film is deposited. Thepolycrystalline silicon film is deposited by the low pressure CVD withusing monosilane and phosphine as source materials. The substratetemperature at this time is 580° C. Next, by the low pressure CVD withusing tungsten hexafluoride and dichlorosilane as source materials, atungsten silicide film is formed. The substrate temperature at this timeis 560° C.

Next, the cap insulating film 5 formed of a silicon oxide film isdeposited on the polycide film 4 a. The cap insulating film 5 is formedby the low pressure CVD at 650° C. with using Tetra Ethyl Ortho Silicate(TEOS) and oxygen as source materials. Then, after the dry etching ofthe insulating film 5 with using a photoresist film as a mask, thepolycide film 4 a is dry-etched with using the cap insulating film 5 asa mask. By doing so, the gate electrode 4 is formed on each of thedigital circuit unit and the analog circuit unit and the control gate 41is formed on the flash memory circuit unit. The gate length of the gateelectrode 4 is 0.35 μm at minimum. The control gate 41 has a shape beinglaid over the memory gate 40.

Next, as shown in FIG. 15, the MOS transistors (Qn, Qp) are formed onthe digital circuit unit and the analog circuit unit, and the MONOS-typeflash memory transistors (Qf) are formed on the flash memory circuitunit. First, after impurities are ion-implanted to the p type well 7 andthe n type well 8, a silicon oxide film is formed by the low pressureCVD. Then, by the anisotropic etching of this silicon oxide film, thesidewall 6 is formed on the sidewall of the gate electrode 4.

Next, after the ion implanting of the impurities into the p type well 7and the n type well 8, a heat treatment is performed at 850° C. for 15minutes to activate the impurities by doing so, the source and the drain(diffusion layers 9 and 10) are formed. Also, by the above-described ionimplantation of impurities, a pn junction (not shown) is also formed,and simultaneously a detecting unit of a temperature sensor by a pnjunction diode is formed.

Next, as shown in FIG. 16, after the silicon oxide film 11 having athickness of 700 nm is formed on the upper layer of the transistors (Qn,Qp, Qf) by the plasma CVD using high-density plasma with using TEOS andoxygen as source materials, the silicon oxide film 11 is polished byabout 400 nm by a CMP so as to planarize the surface thereof.

Next, after the contact hole 12 is formed in the silicon oxide film 11by dry etching with using a photoresist film as a mask, the plug 13 isformed inside of the contact hole 12. The plug 13 is formed in themanner as follows. First, a titanium film and a titanium nitride filmare sequentially deposited by the sputtering method, and a heattreatment is performed in a nitrogen atmosphere at 650° C. for 30minutes. With this heat treatment, titanium is reacted with silicon onthe substrate surface to form titanium silicide. Therefore, it ispossible to reduce the contact resistance. Next, after a tungsten filmis deposited by the CVD with using tungsten hexafluoride and hydrogen assource materials, the titanium film, the titanium nitride film, and thetungsten film are etched back. Also, these films may be polished by aCMP instead of the etch back.

Next, as shown in FIG. 17, the first layer wiring 14, the interlayerinsulating film 23, and the second layer wiring 16 are sequentiallyformed on the silicon oxide film 11. The first layer wiring 14 is formedby sequentially forming an aluminum alloy film containing 0.5% of copperand a titanium nitride film on the silicon oxide film 11 by a sputteringmethod, and then patterning these films by dry etching with using aphotoresist film as a mask. The interlayer insulating film 23 is formedby depositing a silicon oxide film having a thickness of 700 nm by theplasma CVD with using TEOS and oxygen as source materials and thenpolishing its surface by 300 nm to be planarized. Next, by dry etchingwith using a photoresist film as a mask, a via hole 15 is formed in theinterlayer insulating film 23, and then a titanium film, a titaniumnitride film, an aluminum alloy film containing 0.5% of copper, and atitanium nitride film are deposited on the interlayer insulating film 23by a sputtering method. Subsequently, these films are patterned by dryetching with using a photoresist film as a mask. By doing so, the secondlayer wiring 16 is formed.

Next, as shown in FIG. 18, the third layer wiring 18, the fourth layerwiring 20, and the fifth layer wiring 22 are sequentially formed on theupper layer of the second layer wiring 16 via the interlayer insulatingfilm 23. The third layer wiring 18 to the fifth layer wiring 22 areformed in the manner similar to that of the second layer wiring 16. Apart of the fifth layer wiring 22 formed in the pressure detecting unitis the lower electrode 22 a. The shape of the lower electrode 22 aviewed from the top is a circle having a diameter of 37 μm. Also, withthe first layer wiring 14 to the fifth layer wiring 22, the pad 50 isformed on the pad unit.

The semiconductor device embedded with pressure sensor according to thisembodiment has five layer wirings (the first layer wiring 14 to thefifth layer wiring 22). However, the number of layers is not limited tofive, but any number of wiring layers as required may be formed. Also,in the manufacturing method according to this embodiment, the CMP isapplied to the silicon oxide film 11 and all interlayer insulating films23 on the upper layers of the transistors (Qn, Qp, Qf). However,depending on the semiconductor device embedded with pressure sensor tobe manufactured, the uppermost layer wiring (the fifth layer wiring 22)can be approximately planarized even if several CMP processes areomitted. Therefore, it is not always necessary to apply the CMP to allinterlayer insulating films 23.

As described above, except for the CMP process for planarization, theembedding of a pressure sensor does not place any restrictions on thesemiconductor device and the semiconductor device manufacturing method.

Next, as shown in FIG. 19 (a section view of the pressure detectingunit), the silicon oxide film 24 having a thickness of 0.5 μm is formedon the upper layer of the lower electrode 22 a, and the via hole 45 isformed in the silicon oxide film 24 by dry etching with using aphotoresist film as a mask. Then, a tungsten silicide film 26 having athickness of 200 nm, which is a part of the diaphragm, is formed on thesilicon oxide film 24. The silicon oxide film 24 is formed by the plasmaCVD with using TEOS and oxygen as source materials, and the tungstensilicide film 26 is formed by a sputtering method. When the tungstensilicide film 26 is formed, the composition of the sputter target isW:Si=1:2.8, but is not necessarily restricted to this composition. Theflow rate of argon at the time of sputtering is adjusted so that theformed tungsten silicide film 26 has a tensile stress of about 200 MPa.Instead of adjusting the flow rate of argon, stress adjustment can alsobe carried out by, for example, adjusting a substrate temperature at thetime of film formation. The tungsten silicide film 26 immediately afterfilm formation is in a microcrystalline state close to the amorphousstate, and crystals do not grow unless a heat treatment is applied. Inthe semiconductor device embedded with pressure sensor according to thisembodiment, the tungsten silicide film 26 is used as a part of thediaphragm, but another material, for example, a tungsten film is alsoavailable. In the case of a tungsten film, the film is already in acolumn-shaped crystalline state immediately after film formation. Alsoin this case, the stress adjustment of the film can be carried out byadjusting the flow rate of argon or the substrate temperature at thetime of film formation. Furthermore, although not used in thisembodiment, in order to reduce the nonplanar topography, the SOG (Spinon Glass) film formed by the spin coating method can be formed on thesilicon oxide film 24, and then, the tungsten silicide film 26 can beformed on the formed film.

Next, as shown in FIG. 20 (a section view of the pressure detectingunit), many holes 27 are formed in the tungsten silicide film 26 by dryetching with using a photoresist film as a mask. A lithography apparatusfor use at this time is an i-line stepper, and each hole 27 has adiameter of 0.25 μm. When forming the hole 27, a hole having a diameterof 0.45 μm is first opened in the tungsten silicide film 26 throughexposure using an i-line photoresist film, and then, the photoresistfilm is softened by heating that is a known thermal flow technology. Bydoing so, the hole diameter is reduced. Next, the tungsten silicide film26 is dry etched with using the photoresist film having this hole withreduced diameter to form the hole 27.

Next, after the photoresist film is removed, the silicon substrate 1 isimmersed in hydrofluoric acid to remove a part of the silicon oxide film24 with the hydrofluoric acid coming through the hole 27. By doing so,the cavity 25 is formed between the tungsten silicide film 26 to be apart of the diaphragm and the lower electrode 22 a. After the etchingfor a predetermined time, the etching is stopped by means of the waterrinse, and then, the silicon substrate 1 is dried. The shape of thecavity 25 viewed from the top is a circle having a diameter ofapproximately 30 μm. Since the lower electrode 22 a (the fifth layerwiring 22) has the uppermost layer formed of a titanium nitride film,when the cavity 25 is formed in a part of the silicon oxide film 24, thelower electrode 22 a is not etched by hydrofluoric acid.

As described above, the tungsten silicide film 26 has a tensile stress.This can prevent the so-called sticking, which is a phenomenon in whichthe tungsten silicide film 26 is stuck to the lower electrode 22 a by asurface tension of water at the time of drying after water rinse. Thereduction of the size of the capacitor or spacing the lower electrodeand the diaphragm apart from each other may be effective for theprevention of the sticking. However, there is a problem that thecapacitance of the capacitor is reduced. In the capacitor according tothis embodiment, the sticking does not occur.

Next, as shown in FIG. 21 (a section view of the pressure detectingunit), the silicon nitride film 28 is deposited on the tungsten silicidefilm 26, and the silicon oxide film 29 is formed on the silicon nitridefilm 28 by the plasma CVD with using TEOS and oxygen as sourcematerials. When the silicon nitride film 28 is deposited, the hole 27formed in the tungsten silicide film 26 is filled by the silicon nitridefilm 28. This is an effect achieved by the fact that the diameter of thehole 27 is reduced to 0.25 μm by using the technology of a resistthermal flow. Note that, in this embodiment, the hole 27 is filled bythe silicon nitride film 28 by the plasma CVD. The hole 27 can be filledby using another film, for example, a silicon oxide film formed by theatmospheric pressure CVD with using TEOS and ozone as source materialsor a silicon oxide film formed by the plasma CVD using high-densityplasma. When the silicon nitride film 28 is deposited by the plasma CVD,the pressure inside the cavity 25 formed between the tungsten silicidefilm 26 and the lower electrode 22 a is reduced to be vacuum. Whendeposited by the atmospheric pressure CVD, the cavity is filled with gascontaining nitrogen and the like as the main components at atmosphericpressure.

Next, the silicon oxide film 29, the silicon nitride film 28, thetungsten silicide film 26, and the silicon oxide film 24 are patternedby dry etching with using a photoresist film as a mask so that thesefilms are left only on the pressure detecting unit. The pattern of thesefilms left on the pressure detecting unit viewed from the top is acircle having a diameter of 45 μm. Note that, in the circuit of thepressure detecting unit according to this embodiment, nine capacitorsare connected in parallel to achieve a large capacitance for highlyaccurate measurement.

Next, as shown in FIG. 22 (a section view of the pressure detectingunit), after the silicon nitride film 30 is deposited on the siliconsubstrate 1 by the plasma CVD, the photosensitive polyimide film 31 isformed on the silicon nitride film 30 by the spin coating method.

Next, as shown in FIG. 23 (a section view of the pressure detectingunit), after the photosensitive polyimide film 31 on the diaphragm isexposed and developed for removal, the silicon nitride film 30 and thesilicon oxide film 29 on the diaphragm are etched with using thisphotosensitive polyimide film 31 as a mask. By doing so, the hole 32 isformed on the diaphragm. At this time, the photosensitive polyimide film31 and the silicon nitride film 30 on the pad 50 are also etched toexpose the pad 50. As shown in FIG. 2 described above, thephotosensitive polyimide film 31, the silicon nitride film 30, and thesilicon oxide film 29 on the diaphragm of the reference capacitor unitare not etched. Basically, this is the only point that is different fromthe method of manufacturing a pressure detecting unit. Similar to thecapacitors of the pressure detecting unit, nine capacitors are connectedin parallel to achieve a large capacitance also in the referencecapacitor unit.

Through the processes described above, the semiconductor device embeddedwith pressure sensor according to this embodiment shown in FIG. 1 toFIG. 5 is obtained.

The operational characteristics of the semiconductor device embeddedwith pressure sensor manufactured in the above-described manner ismeasured and evaluated. As a result of high-frequency measurement of 100kHz, the capacitance in atmospheric pressure is 184.5 fF as shown inFIG. 24. This value is obtained when nine capacitors with the diameterof a fixed electrode of 37 μm are connected in parallel.

Next, when the capacitance is measured while changing the appliedpressure, the value is changed as shown in FIG. 24. For example, acapacitance value of 202.5 fF is obtained at the pressure of 3 kg/cm².In addition, when deformation of the diaphragm at the pressure of 3kg/cm² is examined, it is found that the diaphragm is dented byapproximately 0.15 μm at the center portion of the capacitor. That is,as a result of the reduction in distance to the fixed electrode by 0.15μm, the capacitance is increased from 184.5 fF to 202.5 fF. Similarly,when the capacitance of the reference capacitor is examined, thecapacitance in atmospheric pressure is 184.7 fF. It is found that thisvalue is not changed even when pressure is applied, and represents thatthe performance required for the reference capacitor is provided. Notethat one information that cannot be obtained only by the comparison withthe reference capacitor is temperature. In the semiconductor deviceembedded with pressure sensor according to this embodiment, however,temperature is obtained from the temperature sensor described above tocorrect the pressure based on the temperature.

Next, a reliability evaluating test is performed. Atmospheric pressureand a pressurized state of 4 kg/cm² are repeated a large number oftimes, and then the capacitance at atmospheric pressure is measured. Theresults obtained by the pressure detecting unit are shown in FIG. 25. Asa result of the measurement up to 100,000 times of repetition ofpressurization, the value of the capacitance is within the range of±0.25%, and an increasing tendency or decreasing tendency due to therepetition of pressurization is not shown. Therefore, the difference canbe considered to be the margin of error including that of the measuringsystem.

Next, a layout of the uppermost layer wiring will be described withreference to FIG. 26 to FIG. 28. In this embodiment, the fifth layerwiring is the uppermost layer wiring. However, depending on thesemiconductor device to be embedded with a pressure sensor, anotherwiring layer may be the uppermost layer wiring. FIG. 26 is a drawingshowing a layout of the pressure detecting unit. Each circular portioncorresponds to a lower electrode 22 b, and its diameter is 37 μm. Thelower electrodes 22 b are electrically connected to each other byconnecting portions 34. The wiring is electrically connected from itsend portion 35 to a lower layer wiring via a via hole (not shown). Thisdrawing shows a layout of the pressure detecting unit, which is exactlythe same as a layout of the reference capacitor unit. Therefore, theparasitic capacitance of the connecting portions 34 or the like of thepressure detecting unit is also equivalent to that of the referencecapacitor unit.

FIG. 27 is a drawing showing a layout of the CMOS circuit unit, in whichpower supply wirings 36 and 37 and others are disposed. The wiring widthof each of the power supply wirings 36 and 37 at this portion is 3 μm.FIG. 28 is a drawing showing a layout of the pad portion. The pad 51 hasa square shape with each side of 70 μm and is connected to the CMOScircuit unit and others via lead wirings 52. Note that, in many flashmemory circuit units, the uppermost layer wiring is not used asdescribed above.

As has been described in detail, according to this embodiment, asemiconductor device can be formed on a layer located lower than thepressure detecting unit. Therefore, it is possible to reduce the chiparea of the semiconductor device embedded with pressure sensor. Otherthan the application and change of a planarization process such as CMPto be performed as required, no influence is exerted on semiconductordevices located lower than the pressure detecting unit. Therefore, norestriction occurs on the manufacturing method of a semiconductordevice. Consequently, it is possible to embed a highly-microfabricatedhigh-performance semiconductor device together with a pressure sensor,and the low power consumption can be achieved. Furthermore, since thepressure detecting unit is formed on an upper layer of a semiconductordevice, and the semiconductor device is protected by a nitride film anda polyimide film, it is possible to simplify the packaging more thanthat of the conventional technologies.

Second Embodiment

In the second embodiment, the present invention is applied to asemiconductor device embedded with pressure sensor in which a digitalcircuit, an analog circuit such as an amplifier for amplifying a sensorsignal and a wireless transceiver circuit, a flash memory circuit of aMONOS type, a capacitive pressure sensor and the like are embeddedtogether on one chip.

As shown in FIG. 29, the silicon oxide film 24 on the fifth layer wiring22, which is the uppermost layer wiring, and the lower electrode 22 a isplanarized by CMP so as to have a height equal to that of the fifthlayer wiring 22 and the lower electrode 22 a. On the upper portion ofthe silicon oxide film 24, the fifth layer wiring 22, and the lowerelectrode 22 a, a silicon oxide film 47 is formed, and the diaphragm isformed thereon. The cavity 25 under the diaphragm is filled with gascontaining nitrogen as the main component at atmospheric pressure, and asilicon dioxide film 46 is formed on the inner wall thereof. A metalfilm to be a part of the diaphragm is a tungsten film 39, and itssurface is oxidized. Furthermore, a film on a layer upper than thetungsten film 39 is the silicon oxide film 46, and the silicon nitridefilm 30 and the photosensitive polyimide film 31 are formed on the upperportion thereof. The pressure detecting unit according to thisembodiment has the structure excellent in flatness when compared withthe pressure detecting unit according to the above-described firstembodiment.

Next, a method of manufacturing the semiconductor device embedded withpressure sensor according to this embodiment will be described withreference to FIG. 30 to FIG. 32.

First, as shown in FIG. 30, after the first layer wiring 14 to the fifthlayer wiring 22 and the lower electrode 22 a are formed on the siliconsubstrate 1 in the same manner as that of the first embodiment, thesilicon oxide film 24 having a thickness of 3 μm is deposited on theupper layer of the fifth layer wiring 22 and the lower electrode 22 a bythe plasma CVD using high-density plasma. Subsequently, the siliconoxide film 24 is polished by a CMP. By doing so, the surfaces of thefifth layer wiring 22 and the lower electrode 22 a are exposed. Then, asilicon oxide film 47 is deposited on the upper portion of the siliconoxide film 24, the fifth layer wiring 22, and the lower electrode 22 aby the CVD.

In view of the local distribution of CMP polishing speeds, it isdesirable that the titanium nitride film of the fifth layer wiring 22and the lower electrode 22 a is made in advance thicker than normal (forexample, 0.25 μm). Next, after the via hole 45 is formed in the siliconoxide film 24, the tungsten film 39 having a thickness of 200 nm isdeposited on the silicon oxide film 24 by the plasma CVD with using TEOSand oxygen as source materials. Similar to the tungsten silicide film inthe above-described first embodiment, film formation conditions aredefined so that the tungsten film 39 has a tensile stress.

Next, as shown in FIG. 31, by a lithography technology using anelectron-beam lithography apparatus and well-known dry etchingtechnology, many holes 27 each having a diameter of 0.2 μm are formed inthe tungsten film 39. Similar to the above-described first embodiment,the holes 27 may be formed with the concurrent use of the i-linelithography technology and the resist thermal flow technology, and theirdiameter is desirably reduced to be about 0.3 μm or smaller. Also,according to need, a pattern may be once transferred from a resist to ahard mask, and then the holes 27 may be formed in the tungsten film 39using the hard mask. When a silicon oxide film is used as the hard mask,the hard mask is simultaneously removed at the time of forming thecavity 25 with using hydrofluoric acid at the next process, which isadvantageous.

Next, by the etching using hydrofluoric acid, the cavity 25 is formed inthe silicon oxide film 47. Similar to the above-described firstembodiment, etching is performed with the tungsten film 39 left on thefront surface of the silicon substrate 1 instead of performing theetching by hydrofluoric acid with using a photoresist film as a mask.This is because resistance of the photoresist film to hydrofluoric acidis taken into consideration. If the photoresist with high resistance isused, it is also possible to process the tungsten film 39 in advance.Similar to the above-described first embodiment, also in thisembodiment, the sticking does not occur in the course of water rinse anddrying after the etching owing to the effect of the tungsten film 39having a tensile stress.

Next, as shown in FIG. 32, the silicon oxide film 46 having a thicknessof 200 nm is deposited by the atmospheric pressure CVD with using TEOSand ozone as source materials. In an early stage of depositing thissilicon oxide film 46, an exposed portion of the tungsten film 39 isoxidized, and the anti-corrosion characteristic thereof is improved.Also, when the silicon oxide film 46 is deposited, since the atmosphericpressure CVD with using TEOS and ozone as source materials is used, thesilicon oxide film 46 is formed even on the inner wall of the cavity 25.The silicon oxide film 46 on the inner wall of the cavity 25 has aneffect to prevent the tungsten film 39 of the diaphragm and the lowerelectrode 22 a from being short-circuited when an excessive pressure isapplied to the pressure detecting unit. Furthermore, since the siliconoxide film 46 is formed by the atmospheric pressure CVD, the inside ofthe cavity 25 is filled with gas containing nitrogen as the maincomponent at atmospheric pressure. The processes thereafter areidentical to those in the above-described first embodiment. In theforegoing, the method of manufacturing the pressure detecting unit hasbeen described. Also, the reference capacitor is manufactured in analmost the same manner.

Many semiconductor devices embedded with pressure sensor according tothis embodiment are manufactured, and their characteristics aremeasured. As a result, variation in capacitance value under atmosphericpressure is smaller than that in the above-described first embodiment.This is because, since the silicon oxide film 24 on the upper layer ofthe fifth layer wiring 22 and the lower electrode 22 a is planarized,the processing accuracy in the following diaphragm formation isimproved. The other characteristics are similar to those in theabove-described first embodiment.

Third Embodiment

In the third embodiment, the present invention is applied to asemiconductor device embedded with pressure sensor in which a digitalcircuit, an analog circuit such as an amplifier for amplifying a sensorsignal and a wireless transceiver circuit, an EEPROM circuit, acapacitive pressure sensor and the like are embedded together on onechip.

A method of manufacturing a pressure detecting unit according to thisembodiment will be described with reference to FIG. 33 to FIG. 37.First, the first layer wiring 14 to the fifth layer wiring 22 and thelower electrode 22 a are formed on the silicon substrate 1 in the samemanner as that of the above-described first embodiment, and then, asshown in FIG. 33, a silicon nitride film 53 on the silicon substrate 1is patterned so that the patterned silicon nitride film 53 is left onthe upper portion and the periphery of the lower electrode 22 a. Then, asilicon oxide film 54 is deposited on the silicon substrate 1, and thesurface of the deposited film is planarized by a CMP. Thereafter, asilicon oxide film 55 is formed on the upper portion of the siliconoxide film 54.

Next, as shown in FIG. 34, the silicon oxide films 54 and 55 in theperiphery of the lower electrode 22 a are removed by dry etching withusing a photoresist film as a mask. At this time, the via hole 45 isformed on the upper portion of the fifth layer wiring 22.

Next, as shown in FIG. 35, the tungsten silicide film 26, which is apart of the diaphragm, is deposited by the sputtering method. At thistime, the substrate temperature is set at about 300° C. so as to makethe tungsten silicide film 26 have a tensile stress of about 250 MPa.Then, the hole 27 is formed in a part of the tungsten silicide film 26by dry etching with using a photoresist film as a mask.

Next, as shown in FIG. 36, the silicon oxide films 54 and 55 inside ofthe hole 27 are etched by using hydrofluoric acid. By doing so, thecavity 25 is formed between the lower electrode 22 a and the tungstensilicide film 26. This etching is performed to removing all of thesilicon oxide films 54 and 55 between the silicon nitride film 53 andthe tungsten silicide film 26. Therefore, since no precise etching timecontrol is required, the formation of the cavity 25 can be facilitatedin comparison with the above-described first and second embodiments.

Next, as shown in FIG. 37, after the hole 27 is filled by depositing asilicon oxide film 56 on the tungsten silicide film 26, the siliconoxide film 56 is etched so that the silicon oxide film 56 is left onlyinside and in the periphery of the hole 27. The subsequent processes areidentical to those in the above-described first embodiment.

Many semiconductor devices embedded with pressure sensor according tothis embodiment are manufactured, and their characteristics aremeasured. As a result, variation in capacitance value under atmosphericpressure is smaller than that in the above-described first and secondembodiments. This is because, unlike the first and second embodiments,the volume of the cavity 25 can be made always constant withoutdepending on the time of the etching by hydrofluoric acid. The othercharacteristics are similar to those in the above-described firstembodiment.

Fourth Embodiment

In the fourth embodiment, the present invention is applied to asemiconductor device embedded with pressure sensor in which a digitalcircuit, an analog circuit such as an amplifier for amplifying a sensorsignal and a wireless transceiver circuit, an EEPROM circuit, acapacitive pressure sensor and the like are embedded together on onechip.

FIG. 38 is a section view of a pressure detecting unit according to thisembodiment. In this embodiment, the fourth layer wiring 20 is theuppermost layer wiring, and a lower electrode 57 is formed of aconductive layer upper than the uppermost layer wiring. The conductivelayer forming the lower electrode 57 is formed of a tungsten film, analuminum alloy film, or a copper film having a thickness of 100 nmdeposited by, for example, a sputtering method.

In this embodiment, a conductive layer forming the lower electrode 57 isrequired in addition to the wirings. However, in comparison with thecase in which the lower electrode 57 is formed of wiring layer, thelower electrode 57 can be formed to be thinner. Therefore, even if theinsulating film of a layer upper than the lower electrode 57 is notplanarized by the CMP, sufficient planarity can be obtained.

The cavity 25 is formed by etching the silicon oxide film 24 withhydrofluoric acid. Note that, if the silicon oxide film 24 is etchedwith hydrofluoric acid, the lower portion of the cavity 25 (lowerelectrode 57) and the upper portion thereof (tungsten silicide film 26)are stuck to each other in some cases. In such a case, for theprevention of the sticking, a polyimide resin film is used to form theinsulating film between the lower electrode 57 and the tungsten silicidefilm 26 and the polyimide resin is etched by the oxygen plasma ashing.

Fifth Embodiment

FIG. 39 is a section view of a pressure detecting unit according to thisembodiment. In this embodiment, the fourth layer wiring 20 is theuppermost layer wiring, and a planarized silicon oxide film 58 is formedon the upper portion thereof. A silicon nitride film 59 is formed on theupper portion of the silicon oxide film 58. Also, on the upper portionof the silicon nitride film 59, an electrode 91 formed of a conductivelayer upper than the uppermost layer wiring is formed. The electrode 91is formed of, for example, an aluminum alloy film and is connected tothe fourth layer wiring 20 via a via hole 92.

On the upper portion of the electrode 91, a pressure-sensitiveconductive film 93 having a thickness of 5 μm is formed. Thepressure-sensitive conductive film 93 used in this embodiment is formedof a material in which conductive particles are distributed in a basematerial made of an organic material. In more detail, the base materialis an elastomer, and the conductive particles are nickel, but othermaterials may be used. Even with a film in which carbon is used as theconductive particles, it is possible to manufacture a semiconductordevice embedded with pressure sensor similar to that of this embodiment.

In this embodiment, the previously-cut pressure-sensitive conductivefilm 93 is bonded so as to cover the electrode 91. The cutpressure-sensitive conductive film 93 has one surface applied with anadhesive (not shown). With this adhesive, the film can be fixed onto thesurface of the silicon substrate 1 when a protective sheet is peeledoff. Since the adhesive is not present on a portion covering theelectrode 91, no influence is exerted on electric connection between theelectrode 91 and the pressure-sensitive conductive film 93. After thepressure-sensitive conductive film 93 is fixed to a predeterminedposition, an aluminum alloy film 94 is formed on the pressure-sensitiveconductive film 93. Although it is possible to detect pressure evenwithout this aluminum alloy film 94, owing to the presence of this film,it is possible to sensitively detect the changes in resistivity of thepressure-sensitive conductive film 93 by the deformation in a directionvertical to the main surface of the silicon substrate 1. That is, ahighly-sensitive pressure sensor can be achieved. By embedding apressure detecting unit including this aluminum alloy film 94 togetherwith a pressure detecting unit not including this on the samesemiconductor device embedded with pressure sensor, it becomes possibleto detect a wide range of pressure. The aluminum alloy film 94 has thephotosensitive polyimide film 31 formed thereon. Also, thephotosensitive polyimide film 31 is removed from the upper portion ofthe pressure detecting unit to form the opening 32.

FIG. 40 shows one example of a plane layout of the above-mentionedelectrode 91. By measuring the resistance between electrodes 91 a and 91b (or between 91 c and 91 d) facing to each other, the pressure isobtained. In comparison with the distance between the electrodes 91 aand 91 b, the distance between the electrodes 91 c and 91 d is shorter.By measuring the changes in resistance between the electrodes 91 a and91 b and the changes in resistance between the electrodes 91 c and 91 din accordance with the pressure in advance and storing them in thememory unit, it becomes possible to measure the pressure in a widerrange with high accuracy. Also, by obtaining the pressure from anaverage value or a central value measured from many disposed electrodeshaving exactly the same pattern, it becomes possible to measure thepressure without suffering from the influences of partial failures.Furthermore, in addition to the presence or absence of the aluminumalloy film 94 shown in FIG. 39 or the contrivance of the pattern of theelectrodes (91 a to 91 d), two types of pressure-sensitive conductivefilms 93 having different thicknesses or materials can be used on thesame semiconductor device embedded with pressure sensor. By doing so, itbecomes possible to detect the pressure in a wider range with highaccuracy. Note that, in the semiconductor device embedded with pressuresensor according to this embodiment, temperature is obtained from theabove-described temperature sensor to correct the pressure based on thetemperature.

Many semiconductor devices embedded with pressure sensor according tothis embodiment are manufactured, and their characteristics aremeasured. As a result of the measurement, it is possible to measure thepressure with a high degree of reproducibility within a range of 7kg/cm² from the atmospheric pressure. Also, the device is excellent indurability.

In the foregoing, the invention made by the inventors of the presentinvention has been concretely described based on the embodiments.However, it is needless to say that the present invention is not limitedto the foregoing embodiments and various modifications and alterationscan be made within the scope of the present invention.

The present invention can be applied to a semiconductor device embeddedwith pressure sensor.

1. A semiconductor device, comprising: an electronic circuit having MOStransistors formed on a semiconductor substrate and multilevel wiringlayers formed over said semiconductor substrate, and a sensor having afixed electrode, a diaphragm formed over said fixed electrode and acavity formed between said fixed electrode and said diaphragm, whereinsaid fixed electrode of said sensor is formed by using one of saidmultilevel wiring layers of said electronic circuit, and wherein saiddiaphragm of said sensor is formed by using a conductive layer upperthan said one of said multilevel wiring layers.
 2. The semiconductordevice according to claim 1, wherein said electronic circuit comprises adigital circuit and an analog circuit, and wherein said sensor is formedabove a formation area of said digital circuit.
 3. The semiconductordevice according to claim 2, wherein said sensor is not formed above aformation area of said analog circuit.
 4. The semiconductor deviceaccording to claim 1, wherein said sensor detects pressure by measuringa capacitance between said fixed electrode and said diaphragm.
 5. Thesemiconductor device according to claim 1, wherein said device isinstalled in a tire and is used for detecting pressure inside said tire.6. The semiconductor device according to claim 1, wherein said diaphragmcomprises a tungsten silicide film or a tungsten film.
 7. Thesemiconductor device according to claim 6, wherein said tungstensilicide film or said tungsten film has a tensile stress.